Long-term changes in the frequency of cyclones and their trajectories in Central and Northern Europe

Abstract

Changes in the number of cyclones and cyclone trajectories in Central and Northern Europe during 1948–2000 are analysed using a database of cyclones. Two hypotheses are advanced. Firstly, the number of cyclones reaching Northern Europe has increased, causing a transition to a more maritime climate. Secondly, the trajectories of cyclones have moved northward, causing the advection of warm and moist air to Northern Europe and decreasing precipitation in Central Europe. These advances were confirmed by data analysis. A linear trend and its statistical significance (P<0.05) for the frequency of cyclones in the Atlantic–European sector (30°W–45°E, 35–75°N) were calculated. Circles with radii of 500, 1000, 1500 and 2000 km with centre coordinates 60°N and 22.5°E were generated. All the cyclones whose centres were located within these circles were counted. Also two meridians −5°E and 20°E – were selected and all the cyclones were counted whose centres crossed the meridians from west to east in the interval of 45–75°N. Changes in the frequency of long-term cyclones were analysed. The number of cyclones reaching Northern Europe has increased in the period 1948–2000. The number of cyclones over the Baltic Sea has increased, especially in the winter. In Central Europe, the number of cyclones has decreased, especially in the warm half-year. The number of long cyclones has increased over the Baltic Sea, especially in the cold half-year.

Recent Change—Sea Level and Wind Waves

“…4.3). This is in good agreement with findings on changes in cyclone trajectories above the Baltic Sea (Sepp et al 2005;Jaagus et al 2008). The magnitude of an expected extreme event at a given location is usually described by the magnitude of the expected maximum extreme event over a certain period, such as 100 years or 1000 years.…”

Changes in storminess on the western coast of Estonia in relation to large-scale atmospheric circulation

“…A northward shift of the winter storm track has been observed during recent decades (Orlanski 1998, Sickmöller et al 2000, McCabe et al 2001. Consistent with these studies, the number of cyclones passing the Baltic Sea region in winter has increased during the second half of the 20th century (Sepp et al 2005).…”

An abrupt change in winds that may radically affect the coasts and deep sections of the Baltic Sea

“…This maximum in the long-term course of wave height occurs synchronously with an extremely large number of days per annum with low pressure in Härnösand, Sweden, a phenomenon that Soomere (2013) seems to take place once or twice a century and that happened in the 1990s (Bärring & von Storch 2004). This phenomenon matches the overall tendency between 1948 and 2000 for the trajectories of cyclones reaching Northern Europe to move northward (Sepp et al 2005). These 2 features can be interpreted (albeit somewhat speculatively) as reflecting a process during which the storm cyclones predominantly cross the Baltic Sea at latitudes of about 62 to 63°N.…”